Magnetically influenced Fe ₃ O ₄ /water flow in heated tubes with sinusoidal twisted tape turbulators: Thermal and hydraulic performance

This study numerically investigates the hydrothermal performance of laminar Fe3O4/water flow in heated tubes equipped with sinusoidal and simple twisted tape turbulators under a transverse magnetic field. Simulations were performed using ANSYS Fluent for three Reynolds numbers (Re = 200, 300, and 400) and magnetic field intensities of 600–2000 G. In the absence of a magnetic field, the sinusoidal turbulator increased the average Nusselt number by 5.01%, 2.50%, and 2.49% over the simple design at Re = 200, 300, and 400, respectively. The application of a magnetic field altered this trend; at Re = 400, the sinusoidal turbulator achieved a Nusselt number up to 7.55% higher than its simple counterpart. While the magnetic field enhanced thermal performance, it also increased the hydraulic resistance, as reflected by the friction factor and pressure-loss trends. While the magnetic field enhanced thermal performance, it also increased the friction factor by more than 60% as Re increased from 200 to 400. The performance evaluation criterion (PEC) revealed an optimal value of 1.67 for the sinusoidal turbulator at Re = 200 and a magnetic field intensity of 2000 G. However, at Re = 300 and 400 with lower field intensities (600–1200 G), the simple turbulator showed a PEC advantage of up to 12.28%. These results highlight the strong coupling between the flow regime, turbulator geometry, and magnetic field strength, and they offer specific design guidance for compact heat exchangers and energy systems.